A comparison of the analgesic effect of oxymorphone by rectal suppository and intramuscular injection in patients with postoperative pain.

The relative analgesic potency of oxymorphone by rectal suppository and intramuscular injection was evaluated in a double-blind, twin-crossover comparison of graded single doses in 136 patients with postoperative pain. The time-effect curves of the two routes of administration differed substantially; rectal resulted in lower and more delayed peak analgesia and a longer duration of action than intramuscular administration. When both duration and intensity of analgesia are considered (total effect), rectal oxymorphone was 1/10 as potent as the intramuscular form; in peak effect, it was only 1/16 to 1/20 as potent. However, because intramuscular oxymorphone is nine to ten times as potent as intramuscular morphine, 5 to 10 mg oxymorphone by suppository provides analgesia comparable to that provided by the usually used doses of parenteral narcotics. Rectal oxymorphone produced no more, and perhaps somewhat fewer, side effects than doses of intramuscular oxymorphone producing equivalent total analgesic effect. None of the patients objected to the rectal route of analgesic administration. This study demonstrates the feasibility of well-controlled analgesic assays employing the double-dummy technique to compare suppositoreis with oral or parenteral analgesic dosage forms. Our observations also suggest that the rectal route is an acceptable and practical way of administering potent analgesics and is probably being underutilized by physicians in the control of moderate to severe pain.